Add 1 cup of Dolomite lime per 10 square feet and water into the soil. Areas with naturally alkaline soils will have naturally pink Hydrangeas. To make flowers blue, add wettable sulfur to the soil, at a rate of 1/2 cup of wettable sulfur per 10 square feet. Water in. Areas with naturally acidic soil will have naturally blue Hydrangeas. Some hydrangeas are not soil sensitive such as this popular species "Nikko Blue". Always ask if it is soil sensitive when purchasing your plant.